Valves, Types and Operations

Prepared by

Osama Hasan

Intern ‘11 Batch 03 (Enven 1.3) Engro Fertilizer

Outline



Valve

 Construction



Types

 Gate, Globe, Plug, Ball, Diaphragm, Check



Operations

 Fouling, Stem Breakage, Packing Leakage,

Valve



Mechanical devices that are used in

industrial piping for flow control by varying

the pipe opening in three positions:

 Fully opening

 Fully closed and

Construction

 Body; connected to the pipe  Bonnet; mounted on the

body to form a tight enclosure

 Stem; attached the structure

(gate or disk) that resist the flow

The body of the valve is flanged with bolt holes in them to be held together with pipe; with a gasket in between to provide a

Construction

 Gate or Disk; controls the

opening

 Stuffing Box; located in

bonnet and filled with

packing, holds the stem and avoids leaks

 Hand Wheel; lifts gate or disk

on rotating and vice versa

 Seat Rings; perpendicular to

flow, make close fit with valve for complete shut down

Construction

 Yoke (For OS & Y);

supports hand wheel and bushing

 Flange (for NRS only);

resists the stem to move up or down

Valves are characterized by the way they resist the

Types

Gate Valve

Globe Valve

Plug Valve

Ball Valve

Diaphragm Valve

Butterfly Valve

Check Valve

Gate Valve



Regulates flow by placing a metal gate or

disc across the opening of pipe.

 the gate has to be strong enough to

withstand the pressure of flow. 

Gate valves are of two types:

 Outside Stem and Yoke (OS & Y) and  Non-Rising Stem (NRS)

OS & Y Gate Valve

 Stem is Threaded at the

hand wheel and

screwed through stem bushing

 Solidly connected with

the hand wheel and turns along with it

 Bottom is solidly

connected to the gate,

OS & Y Gate Valve



The hand wheel and

bushing are also

supported by an

outside yoke.



Stem can be seen

when the valve is

open, therefore needs

NRS Gate Valve



Stem threaded on

the bottom, with a

gate threaded on

the inside.



Used in areas,

where not much

overhead

NRS Gate Valve



The part of the stem

that passes through

the bonnet has a

flange on it, due to

which the stem cannot

move up or down;

instead engages the

gate on turning wheel

and pulls it up or down

and vice versa.

Types of Gate



Solid wedge gate



Parallel disc gate and

Solid split gate

Solid Wedge Gate

 Made of one part and

bears pressure of the flow on one side only.

 Complete shut off is

accomplished through a close fit between gate and seat rings.

 On lowering or raising of

gate there is more friction between gate and seat

rings which tends to wear

out one seat rings quicker (against the side of flow).

Parallel Disc Gate

 Made out of many parts.  When lower wedge or

spreader reaches the stop, it forces the upper spreader to the lower one.

 This pushes the discs outward

against the seat rings and ensures a very tight closing.

 Although one side of disc is

more worn but tight closing

produced by the wedging action, it still allows complete shutoff.

Parallel Disc Gate



The discs are attached to

the spreader in such a

way that they rotate when

the gate is raised or

lowered, this causes an

even wear.



As the upper wedge is

raised, it releases the

wedging pressure and

Parallel Disc Gate



On high temperatures,

pipe expansions can

wrap the body of the

valve, causing extreme

pressure on the gate.



These gates are not used

with material with coarse

particles and in vertical

positions.

Solid Split Gate



A solid split gate is made of one piece,

with flexible outer edges. These edges

bear pressure on the gate when a valve

body wraps up.

Gate Valve Malfunction

 Gate valves malfunction due to erosion of

gate or seat rings which makes tight closure difficult.

 This happens due to the friction between gate

and seat rings on rising or dropping the gate very often.

 It could be avoided by using gate valves in

pipes who are not much disturbed during

normal operation i.e. are completely open or completely closed.

Globe Valve

 The line of flow changes

its direction, which

creates higher pressure

drop and turbulence.  Seat rings are parallel to

the line of flow and stem guides the disc into the seating. Opening is

controlled by a disc.

 Flow starts as soon as the

contact of disc and seat is broken.

Globe Valve

 Very little wear due to

friction and even wear; however partial opening of valve exposes all parts of disc to flow.

 Even wear permits

complete closure even after long use.

 Flow from under the disc

creates less turbulence than flow from the disc.

Globe Valve



Globe valves are also

installed on turnings,

called Angle Globe

Valves.



Flow through angle

valve has fewer

changes of direction

and therefore is less

Types of Disc



Three types of disc are used in globe

valves:

 Plug disc

 Composition disc and

Plug Disc



Cone shaped

Used for heavy

throttling service



Continues to give

positive shut off even

after some wear

Composition Disc

 Made of softer materials.

 When completely closed,

seat ring can make a

contact with the soft part of disc.

 Fine particles in flow

often accumulated on seats or discs can be

embedded on the soft part of the disc ensuring

Conventional Disc



Smaller disc-to-seat

area than plug discs.



Can crush small

particles more easily

but if nicked or worn,

tight closure is not

Plug Valve

 Controls the opening

through a hollow plug,

which is turned/rotated and aligned with the pipe to

permit a straight line of flow.

 Plug is turned a quarter turn,

to stop the flow.

 The valve can be opened

or closed more quickly than previous examples and

produce little turbulence and pressure drop

Plug Valve

 Friction develops between

the body and the plug,

which wears the plug giving it a loose fit.

 The shank of the plug has a

lubricant fitting that makes it possible to apply special lubricant to the plug itself. Lubrication is done often to reduce friction and also

Ball Valve

 Good shut-off

capabilities.

 Quarter-turn (90°)

completely opens or closes the valve.

 Minimal valve operation time and decreases the

likelihood of leakage due to wear from the gland seal.

Ball Valve



Ball valves can be divided into two

categories:

 Reduced bore: valve opening is smaller

than the diameter of the piping

 Full bore: valve opening is the same size as

the diameter of the piping.

 valued because they minimize the pressure

Ball Valve

 Recommended for use in the fully open or fully closed position.

 Not suited to regulate flow by being kept

partially open because ball valves make use of a ring-shaped soft valve seat.

 When used in the partially open position,

pressure is applied to only a portion of the

valve seat, which can cause it to deform.

 If deforms, its sealing properties are impaired

Diaphragm Valve

 ‘Pinching' method to stop the

valve flow using a flexible diaphragm.

 Available in two types:

 Weir and  Straight-way

 The most common is the

weir-type because the straight-way type requires additional

stretching, which can shorten the diaphragm's life-span.

Diaphragm Valve

 Advantages:

 Valve components can be isolated from the process

fluid.

 Construction helps prevent leakage of the fluid

without the use of a gland seal (packing)

 Disadvantages:

 Diaphragm becomes worn more easily  Regular maintenance is necessary

 Not suited for very high temperature fluids  Mainly used on liquid systems.

Check Valve

 Ensure that flow goes in desired direction and

does not reverses.

 Valve is automatically

opened by the flow

pressure and is closed

when the pressure falls.

 It allows flow from one

side only, and on reverse flow, disc gets closed

Lift Check Valve

 Similar to globe valve

structure, with flow raising

the disc and gravity pulling it down.

 Direction of flow is always

kept from under the disc to minimize turbulence.

 It works in both horizontal

and vertical positions, but with slight structural modifications.

Ball Check Valve



A check valve with

flow not in a straight

line.



Similar to lift check

valve with the disk

replaced with a ball.

Operations



Accumulation of Sludge/ Fouling

 Incomplete shut off / opening

 Remedy:

 Addition of Anti fouling sludge  Dismantling of Valve

Operations



Stem Breakage

 Replacement of Valve

 Else Raising the Stem

 By using a Jack Screw  By using over had hoist

Operations

Raising the Broken Stem by

using a Jack Screw

Operations

Raising the Broken Stem by

using an Overhead Hoist

Operations



Packing Leakage

 Opening the valve to max. limit

 Achieving Back-Seating

Operations

Thank You

Prepared by Osama Hasan

School of Chemical and Materials Engineering (SCME) National University of Sciences and Technology (NUST)